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We use the National Longitudinal Survey of Youth, 1979 to study the relationships between married men's earnings and marriage and spouse characteristics. We test three theories posited in the literature to explain these relationships--selection, specialization, and cross-productivity. While previous research finds evidence in support of all three explanations, we argue that the empirical models used are underspecified resulting in biased tests of the theories. We estimate a more complete model, encompassing all three theories. We find evidence in support for the selection and specialization hypotheses, but little support for the cross-productivity hypothesis.